Spray Synthesis of CuFeO2 Photocathodes and In-Operando Assessment of Charge Carrier Recombination

Semiconducting delafossite-phase CuFeO2 is a promising photocathode material for solar-driven hydrogen production given its suitable energy levels and established robustness for photoelectrochemical water reduction. Nevertheless, reported methods for preparing CuFeO2 thin films are cumbersome, and an explanation for the observed poor performance of this material remains under debate. Herein, a facile and scalable deposition method based on aerosol-assisted chemical vapor deposition of CuFeO2 photocathodes is reported. Optimization of deposition conditions reveals that larger grain size is beneficial for photoelectrochemical operation. Extensive photo-electrochemical testing including illumination and potential modulation spectroscopy of these photocathodes under non-sacrificial operation conditions indicates solar photocurrent densities up to 2.5 mA cm(-2). The bulk charge separation efficiency and the interfacial charge injection efficiency at +0.4 V vs RHE are estimated to be 11% and 0.8%, respectively. This establishes that, while bulk photogenerated charge carrier recombination in CuFeO2 remains an important loss, the performance bottleneck of CuFeO2 for H-2 production is clearly due to surface recombination.